Powertrain for a vehicle and method for carrying out load changes

This application is a National Stage completion of PCT/EP2014/052684 filed Feb. 12, 2014, which claims priority from German patent application serial no. 10 2013 204 227.2 filed Mar. 12, 2013.

The present invention concerns a drive-train for a. In addition the invention concerns methods for carrying out a powershift between a frictional shifting element and an interlocking shifting element, in particular in the drive-train according to the invention.

Drive-trains with automated transmissions are known, that use interlocking shifting elements with which, however, only shifts with traction force interruption are possible. In addition drive-trains with powershift transmissions such as dual-clutch transmissions and automatic transmissions are known, in which frictional shifting elements are used in order to carry out shifts while maintaining the traction force.

For example, from the document DE 199 17 724 A1 a drive-train for a motor vehicle is known. The drive-train comprises an electric motor and a two-gear transmission that comprises two loose wheels mounted to rotate on a shaft and which can be engaged by two associated disk clutches in order to transmit torque at an intermediate axle differential to the drive input of the vehicle.

In powershift transmissions, for safety reasons frictional shifting elements are designed as disk clutches that are held open, or ‘normally open’, i.e. which open under spring force so that if the actuating system fails the blocking of the transmission due to two simultaneously engaged gears is prevented. On the other hand, this means that a shifting element of this type has to be permanently kept in its engaged condition by an actuator. Since the clutch rotates, the transmission of rotation for example by virtue of axial bearings or hydraulic rotary ducts is necessary. However, such rotary transmissions give rise to losses that are responsible for substantial efficiency losses, particularly in the case of electric drives.

Consequently, the purpose of the present invention is to propose a drive-train and methods of the type described at the start, with which powershifts can be carried out safely and with the highest possible efficiency.

According to the invention these objectives are achieved by the characteristics and advantageous design features as described in the description and the drawings.

A drive-train for a vehicle is proposed, in particular for a motor vehicle with at least one electric drive, which can be coupled by way of a driveshaft to at least a first gear ratio stage and a second gear ratio stage. Associated with the gear ratio stages there is at least one shifting mechanism for engaging the gear ratio stages. According to the invention, an interlocking shifting element and at least one frictional shifting element are provided as the shifting mechanism. To carry out powershifts, in the proposed drive-train it is provided that each of the gear ratio stages can be engaged with the interlocking shifting element and at least one of the gear ratio stages can be engaged with both the interlocking shifting element and also the frictional shifting element.

Consequently, with the drive-train proposed according to the invention a shifting mechanism of virtually dual design with an interlocking and a frictional shifting element is used, such that the powershift is carried out with the help of the frictional shifting element and once the shift has been completed, the interlocking shifting element can take over the efficiency-optimized torque transmission.

The drive-train is not limited to two-gear transmissions. It is possible without problems also to provide further gear planes or planetary gearsets with additional shifting elements. For example, between the drive unit and the driveshaft a preliminary gear or the like can be arranged, in order to reduce the rotational speed level at the driveshaft.

The transmission ratio stages provided in the drive-train according to the invention can be spur gear stages, planetary gearsets or suchlike. As the interlocking shifting element preferably a claw clutch can be provided, which is preferably in the form of a double claw clutch in order to give two further shift positions in addition to the neutral position. It is also conceivable to use single-action shifting elements.

As the frictional shifting element a disk clutch can preferably be used, which in its non-actuated, starting position is held open, for example by spring force. Other disk clutches too can be used.

Furthermore, methods are also proposed for carrying out a powershift between a frictional shifting element and an interlocking shifting element, in particular in the drive-train according to the invention.

In a powershift from the closed frictional shifting element to the open interlocking shifting element, the meshing movement can be monitored by a path sensor.

For example, the frictional shifting element can be opened when, on the basis of the meshing movement detected, complete meshing is recognized. But for instance, if the meshing movement detected leads to the recognition of a tooth-on-tooth position at the interlocking shifting element, the frictional shifting element can be opened slowly in order to produce a rotational speed difference. Once this rotational speed difference has been produced, the closing of the interlocking shifting element is resumed and the frictional shifting element is then opened when the meshing movement has been completed. As an emergency measure, to resolve a tooth-on-tooth position a load reduction can be carried out until complete meshing has occurred.

If on the basis of the meshing movement detected, partial meshing of the interlocking shifting element is recognized, the interlocking shifting element can be opened again and the frictional shifting element can be partially opened to produce a slipping condition and then closed again, so that a new orientation is reached in the interlocking shifting element to resolve the tooth-on-tooth position.

In an alternative method according to the invention, a strategic decision can be made whether the frictional shifting element or friction clutch should remain closed in the second gear, therefore accepting the actuator losses, or whether the change from the frictional shifting element to the interlocking shifting element should take place.

A forward-looking strategy in the context of the method can provide that the carrying out of a powershift depends on an evaluation of vehicle data and/or topographical data.

A further alternative method can provide that the frictional shifting element is kept closed after a gearshift until a load reduction or a load change from traction loading to thrust loading is carried out, in order then to carry out a load-free powershift between the frictional shifting element and the interlocking shifting element.

Below, the invention is explained further with reference to the drawings, which show:

FIG. 1 : A schematic view of a first embodiment variant of a drive-train according to the invention, with spur gear stages that can be engaged on the driveshaft side as transmission ratio stages;

FIG. 2 : A schematic view of a second embodiment variant of the drive-train according to the invention, with spur gear stages that can be engaged on the intermediate shaft side as transmission ratio stages;

FIG. 3 : A schematic view of a third embodiment variant of the drive-train, with transmission ratio stages in the form of a planetary gearset;

FIG. 4 : A schematic view of a fourth embodiment variant of the drive-train, with two frictional shifting elements associated with the transmission ratio stages; and

FIG. 5 : A schematic view showing various conditions in relation to which various procedures according to the invention are described.

FIGS. 1 to 4 show as examples various embodiment variants of a drive-train for a vehicle according to the invention, in particular a motor vehicle. As its electric drive the drive-train comprises an electric machine EM, which drives a driveshaft 2 directly or via a preliminary gear 1 . In addition at least two transmission ratio stages i 1 and i 2 are provided, which are connected by way of an intermediate shaft 3 to a drive output differential 4 of the vehicle to drive the drive wheels of the vehicle. Associated with the transmission ratio stages i 1 , i 2 is a shifting mechanism which, for carrying out powershifts, comprises both an interlocking shifting element 5 and a frictional shifting element 6 .

FIG. 1 shows a first embodiment variant of the drive-train according to the invention, in which the transmission ratio stages i 1 and i 2 are in the form of spur gear stages. A loose wheel 7 of the first transmission ratio stage i 1 and a loose wheel 8 of the second transmission ratio stage i 2 are associated with the driveshaft 2 and can be connected to the driveshaft 2 by means of the interlocking shifting element 5 .

In shift position A of the interlocking shifting element 5 the loose wheel 7 , and in shift position B the loose wheel 8 is connected to the driveshaft 2 . The fixed wheel 9 of the first transmission ratio stage i 1 and the fixed wheel 10 of the second transmission ratio stage i 2 are connected by way of the intermediate shaft 3 to the drive output differential 4 for driving the drive wheels of the vehicle. By means of the frictional shifting element 6 the loose wheel 8 of the second transmission ratio stage i 2 can also be connected to the driveshaft 2 in order to enable powershifts.

FIG. 2 shows a second embodiment variant of the drive-train, in which, otherwise than in the first embodiment variant according to FIG. 1 , the loose wheels 7 , 8 of the two transmission ratio stages i 1 and i 2 are associated with the intermediate shaft 3 so that they can be engaged by means of the shifting elements 5 and 6 also associated with the intermediate shaft 3 . This has the advantage that the spur gears of the transmission ratio stages i 1 and i 2 can have larger diameters.

Regardless of which of the two embodiment variants is concerned, for example a traction upshift from the transmission ratio stage i 1 to the second transmission ratio stage i 2 can be carried out since load uptake takes place by the frictional shifting element 6 and the interlocking shifting element 5 is moved from its shift position A to the neutral position in order to enable a rotational speed adaptation or rotational speed synchronization by the frictional shifting element 6 , until the shifting element 6 has closed. In the closed condition of the frictional shifting element 6 , the interlocking shifting element 5 can be moved to shift position B and the frictional shifting element 6 can be opened slowly, so that then the torque transmission can take place exclusively by way of the interlocking shifting element 5 .

To resolve for example a tooth-on-tooth position at the interlocking shifting element 5 , the frictional shifting element 6 can be opened slowly in order to enable meshing when a rotational speed difference has been produced. Particularly when a disk clutch of the ‘normally open’ type is used as the frictional shifting element 6 , this is only actuated for a short time and thereby only small actuation losses occur.

FIG. 3 shows a third embodiment variant of the drive-train, in which the transmission ratio stages i 1 , i 2 are realized by a planetary gearset 11 . The sun gear 12 of the planetary gearset 11 is connected to the driveshaft 2 . The planetary carrier 13 of the planetary gearset 11 is connected to a drive output stage 14 , which is connected to the drive output differential 4 by way of the intermediate shaft 3 . The planetary carrier 13 can also be connected to the driveshaft 2 by means of the frictional shifting element 6 . The ring gear 15 of the planetary gearset 11 can be connected by means of the interlocking shifting element 5 to the driveshaft 2 in shift position B or to the housing 16 in shift position A.

Thus, the two transmission ratio stages i 1 , i 2 are realized by the planetary gearset 11 . In this third embodiment variant as well, the second gear can be engaged both by the interlocking shifting element 5 and by the frictional shifting element 6 . In this embodiment variant, by means of the interlocking shifting element 5 and the frictional shifting element 6 various shafts can be connected to one another, such that both act via the same gear so that a direct drive of the planetary gearset 11 can be realized.

FIG. 4 shows a fourth embodiment variant in which, otherwise than in the first embodiment variant according to FIG. 1 , a further frictional shifting element 6 A is provided so that full powershifting ability can be realized, since all the gearshifts can be carried out with the help of the two frictional shifting elements 6 , 6 A so that even overdrive downshifts for recuperation can be carried out as powershifts.

Regardless of the embodiment variants concerned, the design of the drive-train proposed enables a modular concept to be implemented.

Methods based on the drive-train according to the invention for carrying out a powershift between a frictional shifting element 6 , 6 A and an interlocking shifting element 5 are also claimed.

In one method a strategic decision is made whether the frictional shifting element 6 remains closed in the second gear while accepting actuator losses, or whether the shift to the interlocking shifting element 5 should take place. The procedures according to the invention are explained in more detail with reference to the conditions 1 to 3 illustrated in FIG. 5 , wherein for example the interlocking shifting element 5 is in the form of a claw clutch.

The condition is described with reference to the initial situation of the interlocking shifting element or claw clutch 5 , in that the claw clutch is in its condition before its meshing movement begins. Condition 1 describes the case when the claw clutch is fully meshed, when by chance the teeth coincide with gaps. Condition 2 describes the case when the claw clutch cannot mesh because a tooth-on-tooth position has occurred. Finally, condition 3 represents the case when, owing to the claw geometry, the claw clutch meshes only partially. In this case, for example, the claws remain stuck on chamfers.

Beginning with the initial situation in which the interlocking shifting element 5 is open and the frictional shifting element 6 , 6 A is closed, driving is for example taking place in the second gear in which the electric drive EM supplies the drive torque. To close the interlocking shifting element 5 this is correspondingly actuated and the meshing movement begins at a rotational speed difference of zero. In condition 1 meshing takes place without problems. In condition 2 the meshing movement is interrupted because a tooth-on-tooth position has occurred. In condition 3 only partial meshing takes place owing to the claw geometry. By virtue of a path sensor of the actuator the conditions 1 to 3 described above can be distinguished.

In condition 1 the frictional shifting element 6 , 6 A can be opened. In condition 2 the frictional shifting element 6 , 6 A is opened slowly so that a rotational speed difference is produced. When the rotational speed difference is beginning, i.e. when an angle change occurs, the claw clutch can mesh when under no load so long as there is enough play until the next tooth flank. As a safety function, the load can be reduced at the electric drive EM when the claw clutch should not mesh completely. This is an emergency measure in rare cases, and involves acceptance of a very brief traction force interruption. In condition 3 the actuator is reversed again so that the claws of the claw clutch are no longer in contact. Then, the frictional clutch or frictional shifting element 6 , 6 A is briefly partially opened, imperceptibly for the driver, and thereby brought to a slipping condition before being closed again, so that the halves of the claw are differently orientated as regards their rotation angle. A renewed attempt to mesh the clutch is then carried out.

For example, in the context of a forward-looking strategy the following can be provided for: when the need for a downshift from the second to the first gear is foreseen, the frictional shifting element 6 can remain closed. For this, vehicle data can be evaluated, for example the driving resistance can be calculated on the basis of an acceleration balance or, in addition, topographical data can be evaluated.

Basically, it can for example be provided that if the driving resistance is expected to be high, for example on an uphill stretch, the frictional shifting element 6 can remain closed and the interlocking shifting element 5 is not engaged, in order to be able to carry out a downshift as the vehicle slows down.

In an alternative method, after a shift from the first to the second gear the frictional shifting element 6 can remain closed until a load reduction or load change from traction loading to thrust loading is carried out by the driver. This enables a load-free shift from the frictional shifting element 6 to the interlocking shifting element 5 without the driver being aware of it. The interlocking shifting element 5 or shifting claws can mesh under load with no problems.

1 Preliminary gear

2 Driveshaft

3 Intermediate shaft

4 Drive output differential

5 Interlocking shifting element or claw clutch

6 , 6 A Frictional shifting element or friction clutch

7 Loose wheel of the first transmission ratio stage

8 Loose wheel of the second transmission ratio stage

9 Fixed wheel of the first transmission ratio stage

10 Fixed wheel of the second transmission ratio stage

11 Planetary gearset

12 Sun gear

13 Planetary carrier

14 Drive output stage

15 Ring gear

16 Housing

i 1 First transmission ratio stage

i 2 Second transmission ratio stage

EM Electric drive

A Shift position

B Shift position